This invention relates to a detector for ionising radiation.
Radiation detectors comprising diamond have been proposed which are optimised for the detection of different types of radiation. For example, radiation comprising heavy particles such as alpha particles is usually absorbed close to the surface of a detector element, so that a radiation detector optimised for the detection of such radiation can be relatively thin. On the other hand, radiation such as beta particles, x-rays or gamma-rays tends to penetrate the material of a detector element to a greater depth and to be absorbed substantially uniformly throughout the bulk of the detector element.
It is an object of the invention to provide a single detector which is able to detect such different types of radiation optimally, or which can provide different types of information about a single type of radiation.
According to the invention there is provided a detector for ionising radiation comprising at least first and second diamond detector elements connected electrically to a common contact, with respective first and second contacts connected to the first and second detector elements, so that the detector simultaneously provides first and second output signals corresponding to radiation incident on the detector elements.
Preferably the first and second detector elements are optimised for the detection of different types of radiation, or for the detection of different parameters of a particular type of radiation.
The first and second detector elements may be formed as respective first and second layers of diamond material in contact with a common metallic or semi-conductor layer.
In a preferred embodiment of the invention, the first layer comprises a relatively thick layer of diamond material and the second layer comprises a relatively thin layer of diamond material.
The common metallic or semi-conductor layer may comprise a material selected from the group consisting of titanium, tungsten, molybdenum and boron doped diamond.
The first layer may have a thickness of between 0.3 mm and 1.5 mm and a collection distance of at least 20 xcexcm, preferably at least 50 xcexcm, and even more preferably a distance of 300 xcexcm or more. The first layer may be optimised for the detection of beta particles, x-rays and gamma rays.
The second layer may have a thickness of between 10 xcexcm and 40 xcexcm and may be optimised for the detection of alpha particles.
The detector may further include respective conductive layers on the outer surfaces of the first and second layers of diamond material, which preferably comprise a material selected from the group consisting of titanium, tungsten, molybdenum and boron doped diamond.
Respective active contacts may be connected to the conductive layers.
The invention also extends to a radiation detector apparatus comprising a detector as defined above, and farther comprising bias means arranged to apply respective bias voltages to the first and second diamond detector elements, and first and second amplifiers having inputs connected to the first and second diamond detector elements and arranged to generate respective first and second amplified output signals corresponding to radiation incident on the detector elements.